1. Field of the Invention
This invention relates to a soft magnetic film which is used, for example, as a lower core layer (upper shield layer) of a thin-film magnetic head of the magnetoresistive(MR)/inductive type, and more particularly, to a soft magnetic film having high resistivity while keeping a high saturation magnetic flux density and also to a thin-film magnetic head of the MR/inductive composite type.
2. Description of the Relates Art
FIG. 3 is an enlarged sectional view showing a conventional thin film magnetic head as viewed from a side facing to a recording medium.
This thin film magnetic head is a so-called MR/inductive composite-type thin film magnetic wherein a read head h1 utilizing a magnetoresistive effect and a write inductive head h2 are built up, as shown, at an end face of a trailing side of a slider constituting, for example, a floating head.
The read head h1 includes a lower shield layer 1 formed of sendust or an Ni--Fe alloy (permalloy), and a lower gap layer 2 formed on the layer 1 and made of a non-magnetic material such as Al.sub.2 O.sub.3 (aluminium oxide), on which a magnetoresistive layer 3 is further formed. The magnetoresistive layer 3 is constituted of three layers including, as viewed from the bottom, a soft adjacent layer (SAL), a non-magnetic layer (shunt layer) and a magnetoresistive layer (MR layer) arranged in this order. The magnetoresistive layer is normally a layer made of a Ni--Fe alloy (permalloy), the shunt layer is a layer made of Ta (tantalum), and the soft magnetic layer is made of a Ni--Fe--Nb alloy.
The magnetoresistive layer 3 has, at opposite sides thereof, a hard bias layer as a longitudinal bias layer. Moreover, an electrode layer 5 made of a non-magnetic conductive material with a small electric resistance, e.g. Cu (copper), W (tungsten) or the like, is formed on the hard bias layer 4. An upper gap layer 6 made of a non-magnetic material, such as aluminium oxide, is further formed as shown.
A lower core layer 20 is formed on the upper gap layer 6 by plating such as of permalloy. In the inductive head h2, this lower core layer 20 function as a leading side core for applying a recording magnetic field to a recording medium. In the read head h1, the lower core layer 20 functions as an upper shield layer. In the read head h1, a gap length (read width) G11 is determined depending on the gap between the lower shield layer 1 and the lower core layer 20.
A gap layer (non-magnetic material layer) 8 made, for example, of aluminium oxide and an insulating layer (not shown) formed of a polyimide or resist material are built up on the lower core layer 20, and a coil layer 9 formed in a coil-shaped pattern is formed on the insulating layer. The coil layer 9 is formed of a non-magnetic conductive material having a small electric resistance, such as Cu (copper). The coil layer is surrounded with an insulating layer (not shown) formed of a polyimide or resist material, and an upper core layer 10 formed of a magnetic material, such as permalloy, is formed on the insulating layer by plating. It will be noted that the upper core layer 10 function as a trailing side core of the inductive head h2 capable of applying a recording magnetic field to a recording medium.
The upper core layer 10 is in face-to-face relation with the lower core layer 20 via the gap layer 8 at facing side of the recording medium as shown, thereby forming a magnetic gap with a magnetic gap length G12, from which a recording magnetic field is applied to a recording medium. Moreover, a protective layer 11 made of aluminium oxide is formed on the upper core layer 10.
In the inductive head h2, an electric current for recording is applied to the coil layer 9, and a magnetic field for recording is applied to the upper core layer 10 and the lower core layer 20 from the coil layer 9. The leakage magnetic field between the lower core layer 20 and the upper core layer 10 at the magnetic gap portion enables one to record magnetic signals in a recording medium such as a hard disk.
With the thin film magnetic head shown in FIG. 3, the lower core layer 20 functions not only as a leading side core of the inductive heat h2, but also as an upper shield layer of the read head h1, so that the lower core layer 20 should have natures as both a core and a shield.
In order to enhance the core function of the lower core layer 20, the read density of signals in a recording medium has to be increased, for which the layer 20 should have a high saturation magnetic flux density.
Moreover, the layer 20 should preferably have a high resistivity. If the resistivity is low, a heat loss caused by an eddy current in a high frequency band increases, thereby presenting the problem that the magnetic field for recording undergoes a non-linear transition shift (NLTS) due to the eddy current loss, thereby degrading recording characteristics.
In order to enhance the shield function of the lower core portion, it is necessary to stabilize a magnetic domain at the lower core layer 20. To this end, the lower core layer 20 should have properties including an appropriate anisotropic magnetic field and a low magnetostriction constant.
In this connection, however, permalloy, which is used to form a conventional lower core layer 20, has a relatively high saturation magnetic flux density (Bs) of about 10 kG (killogausses), but its resistivity (.rho.) is as low as about 30 .mu..OMEGA..multidot.cm along with an anisotropic magnetic field (Hk) being as low as about 30 Oe (oersteds).
In this way, the lower core layer 20 formed of permalloy has such a low resistivity that it could not stand use in high frequency recording. In addition, since the anisotropic magnetic field is so low as mentioned above, the magnetic domain in the lower core layer 20 becomes unstabilized, with the result that the magnetic domain in the MR layer is unstabilized, leading to the problem that bark hausen noises are liable to occur.